Wikipedia has invented a new "variable vowel" symbolized /a:/ which can represent either /æ/ or /ɑː/ as the situation requires. It is thus a sort of archiphoneme or diaphoneme, and is listed alongside /i/ and /u/.

The note (no. 24) for this vowel on the WP page Help:IPA for English explains the vowel in this way: "With common English words like 'bath' and 'fast', a posh British accent will have ɑː while an American accent will have æ. With relatively recently introduced words, such as 'taco', and placenames such as 'Denali', however, nearly the opposite is the case: British English tends to have æ while American English tends to have ɑː"

The word "posh" will have to go - much too subjective to be used in a serious article.The claim about 'taco' and 'Denali' is not backed up by any evidence. In the case of 'taco', CEPD gives /tæk.əʊ,tɑː.kəʊ/. For 'Denali' we have /dəˈnɑː.li/. I can't imagine an English person, confronted with 'Denali' for the first time, pronouncing it as /dəˈnæl.i/. I will have to try to improve this note.

My main problem with this "diaphonemic" system of WP is that it isn't properly explained. How many users of WP are going to understand that /a:/ is not to be used except where /æ/ and /ɑː/ are in free variation (where the distinction between them is neutralized)? It requires a grasp of the principle that it would be OK to transcribe 'bath' as /baːθ/ but not OK to transcribe 'cat' as /kaːt/.